From b03600fb4f79c55b460d5e5b5cd59fee68d6329d Mon Sep 17 00:00:00 2001
From: FunkyFr3sh <cc.red.alert.1@gmail.com>
Date: Tue, 13 Sep 2022 07:41:01 +0200
Subject: [PATCH] #101 clear backbuffer on flip

---
 inc/IDirectDrawSurface.h | 1 +
 inc/dd.h                 | 1 +
 src/config.c             | 3 +++
 src/ddsurface.c          | 7 +++++++
 4 files changed, 12 insertions(+)

diff --git a/inc/IDirectDrawSurface.h b/inc/IDirectDrawSurface.h
index 97aa39f..f5f897e 100644
--- a/inc/IDirectDrawSurface.h
+++ b/inc/IDirectDrawSurface.h
@@ -21,6 +21,7 @@ typedef struct IDirectDrawSurfaceImpl
     DWORD width;
     DWORD height;
     DWORD bpp;
+    DWORD size;
     DWORD flags;
     DWORD caps;
 
diff --git a/inc/dd.h b/inc/dd.h
index 45dea1c..0c6219c 100644
--- a/inc/dd.h
+++ b/inc/dd.h
@@ -146,6 +146,7 @@ typedef struct CNCDDRAW
     int fixchilds;
     BOOL fixwndprochook;
     BOOL fixnotresponding;
+    BOOL flipclear;
     BOOL locktopleft;
     BOOL d3d9linear;
     BOOL gdilinear;
diff --git a/src/config.c b/src/config.c
index f4af46e..76f6e44 100644
--- a/src/config.c
+++ b/src/config.c
@@ -39,6 +39,7 @@ void cfg_load()
     g_ddraw->fixpitch = cfg_get_bool("fixpitch", TRUE);
     g_ddraw->fixchilds = cfg_get_int("fixchilds", FIX_CHILDS_DETECT_PAINT);
     g_ddraw->fixwndprochook = cfg_get_bool("fixwndprochook", FALSE);
+    g_ddraw->flipclear = cfg_get_bool("flipclear", FALSE);
     g_ddraw->novidmem = cfg_get_bool("novidmem", FALSE);
     g_ddraw->fixnotresponding = cfg_get_bool("fixnotresponding", FALSE);
     g_ddraw->locktopleft = cfg_get_bool("locktopleft", FALSE);
@@ -357,6 +358,7 @@ static void cfg_create_ini()
             "gdilinear=false\n"
             "allow_wmactivate=false\n"
             "dinputhook=false\n"
+            "flipclear=false\n"
             "bpp=0\n"
             "\n"
             "\n"
@@ -491,6 +493,7 @@ static void cfg_create_ini()
             "[CARMA95]\n"
             "renderer=opengl\n"
             "noactivateapp=true\n"
+            "flipclear=true\n"
             "\n"
             "; Carmageddon\n"
             "[CARM95]\n"
diff --git a/src/ddsurface.c b/src/ddsurface.c
index 7e867eb..99eb515 100644
--- a/src/ddsurface.c
+++ b/src/ddsurface.c
@@ -545,6 +545,12 @@ HRESULT dds_Flip(IDirectDrawSurfaceImpl* This, IDirectDrawSurfaceImpl* lpDDSurfa
         InterlockedExchangePointer(&backbuffer->surface, buf);
         InterlockedExchangePointer(&backbuffer->bitmap, bitmap);
         InterlockedExchangePointer(&backbuffer->hdc, dc);
+
+        if (g_ddraw->flipclear)
+        {
+            memset(buf, 0, backbuffer->size);
+        }
+
         LeaveCriticalSection(&g_ddraw->cs);
 
         if (!lpDDSurfaceTargetOverride && This->backbuffer->backbuffer)
@@ -1092,6 +1098,7 @@ HRESULT dd_CreateSurface(
             CreateDIBSection(dst_surface->hdc, dst_surface->bmi, DIB_RGB_COLORS, (void**)&dst_surface->surface, NULL, 0);
 
         dst_surface->bmi->bmiHeader.biHeight = -((int)bmp_height);
+        dst_surface->size = dst_surface->l_pitch * bmp_height * dst_surface->lx_pitch;
 
         if (!dst_surface->bitmap)
         {